The invention is based on an apparatus for recirculating the exhaust gas of an internal combustion engine, having a line leading from the exhaust to the intake side of the engine and a valve for controlling the rate of recirculation disposed in the line.
In order to improve the exhaust gas quality, it is known to provide engines with exhaust gas recirculation systems, in which a bypass line leads from the exhaust to the intake side of the engine. A valve is provided in the bypass line and is triggered in accordance with prespecified criteria in order to adjust the recirculation rate. An apparatus of this general type is known, for instance, from German Offenlegungsschrift No. 29 09 465, corresponding to U.S. Pat. No. 4,333,440.
In the case of cylinder heads with side-by-side valves, the exhaust gas recirculation line is as a rule quite short because of the structural arrangement; in engines with a crosswise cylinder head with opposing valves, however, because of the structural arrangement a relatively long line is required to reach from the exhaust side to the intake side of the cylinder head. If the recirculation rate is set relatively low, for instance during full-load operation, the valve in the exhaust gas recirculation line is closed. As a result, cooling of the exhaust gas then occurs in the recirculation line, causing the formation of condensates. If the recirculation rate is then increased again, the condensate collected in the recirculation line reaches the intake tract of the engine and, together with the cooled exhaust gas component of the clearance volume of the recirculation line, results in indefinite operation of the engine during this transition. However, since engine regulation is based on hot exhaust gas, the consequence is incorrect control of the engine, which in turn makes vehicle operation less smooth and can in fact negate any improvement in the exhaust gas quality that may be attempted by means of exhaust gas recirculation.